Aspects of sedimentation and formation of Bobrikovskian terrigenous and Tulskian carbonate-terrigenous deposits on the western flank of the South Tatar arch

UDK: 551.3.051

DOI: 10.24887/0028-2448-2026-7-12-17

Key words: core, paleo-geography, facies, alluvial-deltaic deposits, distributary, flooding sands, stream mouth bars, spectral decomposition, lithology cube

Authors: R.А. Rakhimzyanov (TatNIPIneft, RF, Almetyevsk); А.М. Каlimullin (TatNIPIneft, RF, Almetyevsk); А.F. Garipov (TatNIPIneft, RF, Almetyevsk); А.V. Plyusnin (Institute of the Earth’s Crust Siberian Branch of the RAS, RF, Irkutsk); P.А. Ryazanov (Almetyevsk State Technological University «Petroleum Higher School», RF, Almetyevsk); А.F. Safarov (TatNIPIneft, RF, Almetyevsk); N.А. Badurtdinova (TatNIPIneft, RF, Almetyevsk); V.G. Bazarevskaya (TatNIPIneft, RF, Almetyevsk); R.R. Аflyatunov (TATNEFT PJSC, RF, Almetyevsk); А.P. Bachkov (TATNEFT PJSC, RF, Almetyevsk); О.М. Ilmukov (TATNEFT PJSC, RF, Almetyevsk)

This paper discusses aspects of sedimentation and formation of Visean deposits within the north part of the western flank of the South Tatar Arch in the Republic of Tatarstan, using the Bobrikovskian terrigenous and Tulskian terrigenous‑carbonate deposits as an example. The study is based on a comprehensive interpretation of cores and well logging data using the isopach maps and 3D seismic interpretation results. Spectral decomposition slices and a number of other seismic attributes were used to update the morphology of facies. Textural and structural features of rocks developed in a certain sedimentation environment were described, ranging from quiet hydrodynamic conditions affected by high tides to active unidirectional hydrodynamics with vigorous supply of sand material, or to fluvial-dominated unidirectional hydrodynamics. Based on the core data, transitional sedimentation environments, ranging from coastal‑continental to shallow‑marine, were identified represented by deltaic macro-facies of the coastal plain: distributaries, flooding sands, deltaic marshes, silting distributaries, deltaic bays, and stream mouth bars; their correlation with the seismic responses on well logs was demonstrated. It was found that formation of complex-genesis traps in the Bobrikovskian-Tulskian deposits was governed by a combination of factors related to paleo-geographic and paleo-geomorphological sedimentation settings at that time. Facies maps were generated for the Bobrikovskian–Tulskian deposits, showing the inheritance of paleo-valley trends of the Tournaisian stage and a local transition from coastal-continental to shallow-marine environments. The obtained results enhance the reliability of geological models and prediction of reservoir zones during exploration planning on the western flank of the South Tatar Arch.

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